The present invention relates to electromagnetic quantity or parameter measurement in conjunction with electrically conductive material at high temperature, wherein an electromagnetic alternating field is generated in connection with the electrically conductive material and a secondary electromagnetic alternating field, responsive to the quantity or quantities to be measured, is generated by induced currents in the electrically conductive material and detected. The electrically conductive material can, for example, be molten metal in, or flowing from a vessel, channel or the like, a continuous rod or billet of metal withdrawn in a continuous casting system, or metal slab or billet during rolling or a similar processing. The quantities which can be subject to measurement (one or more simultaneously) are, for example, a distance to the electrically conductive material, the level of the electrically conductive material, e.g. in a furnace, erosion of the lining, e.g. in a furnace, due to the corroding action of the electrically conductive material, the metallic cross-section of out-flowing molten metal or metal/slag mixture, the cross-section of a metal slab or billet and the resistivity of the electrically conductive material, and thereby its temperature.
In our Swedish patent application Nos. 7605760-3 (corresponding to U.S. Pat. No. 4,138,888), 7605759-5 and 7605761-1, the contents of which are hereby referred to, there are described systems and coil configurations for electromagnetic measurement of quantities such as level, distance, flow and liner erosion in conjunction with electrically conductive liquid material at high temperature, especially molten metal. Although the described measuring systems have been found to function well in practice, there are factors in certain applications which still affect measuring accuracy and usability unfavourably, e.g. the disturbing influence of metal in the surroundings, primarily the plate jacketing or casing of containers, variations in the distance between the measuring coils themselves and to the measured object, and dimensional variations in the measuring coils as well as deficient ambiguity in the measuring signal obtained. The described measuring systems have furthermore certain limitations with regard to the possible applications of electromagnetic measurement.
The object of the present invention is therefore to provide a new method and new apparatus for electromagnetic quantity or parameter measurement of the kind mentioned in the introduction, which supplements the above-mentioned measuring systems and which circumvents the above-mentioned drawbacks and limitations.